The present invention relates generally to private branch exchange (PBX) switches, and more particularly, to a method and apparatus for allowing one or more modules to access voice or data channels on the private branch exchange.
Within a corporate environment, telephone service is typically provided by a private branch exchange switch. A private branch exchange switch is an on-site facility, that is typically owned or leased by a company or another entity. The private branch exchange interconnects the telephones within the facility and provides access to the public telephone system. Typically, a private branch exchange environment uses digital telephone terminals and digital switching. Digital private branch exchange switches were designed to handle analog voice traffic, with the switch performing an analog-to-digital conversion (DAC) so that digital switching can be used internally on the entity premises. Increasingly, however, private branch exchanges (PBX) are carrying data traffic as well as voice traffic. Typically, data calls are generally switched through a modem-pool to the private branch exchange for transmission to the Public Switched Telephone Network (PSTN).
While a private branch exchange allows an entity to efficiently provide access to communication services without necessarily having dedicated telephone lines for each employee, the private branch exchange often limits the types of communications equipment that may be connected to the PBX and the types of services that may be accessed over the PBX. For example, since the telephone terminals connected to the PBX are digital, it is often difficult, if not impossible, to connect an analog device to the PBX. In addition, the communications protocols and hardware specifications of a given private branch exchange are often proprietary to the manufacturer of the PBX. Thus, it is often difficult, if not impossible, to connect equipment manufactured by another manufacturer to the PBX.
Adjunct processors have been proposed for use with private branch exchanges (PBXs) to supplement and enhance the telecommunications services provided by the PBX. For example, a voice mail system is often used with a PBX to provide users with voice messaging capabilities. In order to work together, the PBX and the adjunct processor must be able to communicate with each other. This is typically accomplished by means of a digital control data link, such as the DCIU link, commercially available from ATandT, that interconnects the PBX control processor with the adjunct processor.
In addition, other interfaces have been proposed or suggested that allow other types of equipment to be connected to a private branch exchange. For example, the 8411 terminal, commercially available from Lucent Technologies Inc., of Murray Hill, N.J., provides a tip/ring interface that allows analog devices to be connected to the private branch exchange and an RS-232 (passageway) interface that allows a computer to be connected to the PBX and permits Computer Telephone Integration (CTI). These other interfaces, however, including the 8411 terminal, are typically designed specifically to provide specific features and to operate with the particular communications protocol and/or hardware specification of a given private branch exchange manufacturer, or telephone terminal manufacturer. Current interfaces are unable to support additional features that may be desired by a customer.
As apparent from the above-described deficiencies with conventional techniques for connecting devices to a private branch exchange switch, a need exists for a standard interface to the private branch exchange that allows one or more modules to access voice or data channels on the private branch exchange. A further need exists for an interface to the private branch exchange that utilizes an integrated digital telephone chip. Yet another need exists for an interface to the private branch exchange that permits a module to support additional features for the private branch exchange.
Generally, an application module interface is disclosed that allows one or more modules to access voice or data channels in a private branch exchange environment. In addition, the application module interface provides a number of hardware signals to the telephone terminal and/or modules. The hardware control signals include module present, phone receiving OK and module receiving OK. The module present (MP) signal indicates that a module is plugged into the AMI electrical interface, although the module may not be powered. The module receiving OK (MOD-OK) signal indicates that the module is receiving valid AMI control channel messages. The phone receiving OK (PHONE-OK) signal indicates that the telephone terminal is receiving valid AMI control channel messages.
According to one aspect of the invention, the hardware control signals permit the presence of a telephone terminal and/or a module to be detected, as well as to detect the disruption of an AMI connection. An AMI connection may be disrupted, for example, due to a device losing power, being disconnected or a transient event that corrupts the data stream and causes a loss of synchronization.
According to a further aspect of the invention, the hardware control signals are used to implement a start-up and tear-down mechanism. The module enables its application module interface receiver (AMR) about 30 milliseconds after the module begins the AMI start-up process. The application module interface receiver of the module will not be receiving valid data until the telephone terminal enables its application module interface transmitter (AMX). Thus, the module ignores data errors during this phase of the AMI start-up and only start counting errors after a valid message has been received.
During the initial start-up, the application module interface receiver and the application module interface transmitter of the application module interface in the telephone terminal are off. In addition, the PHONE-OK signal is set to false. Once the phone recognizes that the module present (MP) signal is active, the phone will set the data fields in the application module interface transmitter to zeroes for at least 10 milliseconds, allowing the application module interface receiver of the module to synchronize to the received AMI start bits. After the end of the ten millisecond interval is detected, the phone will begin sending a control channel activity message, once every ten milliseconds.
Meanwhile, when the module receives the first AMI control channel activity message from the telephone terminal, the module will assert its module receiving OK (MOD-OK) signal and enable its application module interface transmitter. The application module interface transmitter of the module is configured to output zeroes in all B and D data fields and no control channel data is sent so that the only ones output are start bits. Thus, the telephone terminal can synchronize to the AMI start bits. The module will then wait until the module receives five link activity messages from the telephone terminal, before the module starts sending its own link activity message at ten milliseconds intervals. In this manner, the telephone terminal can detect the module receiving OK (MOD-OK) signal and enable its application module interface receiver while only start bits are being sent. Forty milliseconds will elapse between the five messages and the telephone terminal needs up to 30 milliseconds to detect the MOD-OK signal and enable its application module interface receiver. Thus, there is a 10 millisecond interval before the module sends its first message.
The telephone terminal detects the MOD-OK signal and enables its application module interface receiver. The telephone terminal continues sending link activity messages every 10 milliseconds. The module starts sending link activity messages every 10 milliseconds after receiving the fifth link activity message from the telephone terminal.
When the telephone terminal detects the receipt of the first link activity message from the module, the telephone terminal will assert the phone receiving OK (PHONE-OK) signal. The PHONE-OK signal indicates that the AMI connection is established and normal message activity may commence. Thus, the telephone terminal reduces the rate of the activity messages to one per 100 milliseconds. In addition, the telephone terminal puts received D channel HDLC data onto its application module interface transmitter (AMX-D=LIUrx-D), and the telephone terminal will allow B channel data onto the application module interface transmitter. It is noted that all AMX-B* data will be zeroes until the module sends a set voice channel configuration message
When the module detects the PHONE-OK signal, the module should reduce its activity message rate to one per 100 milliseconds, and the module may send a phone states request to obtain phone state information. Until the PHONE-OK signal is asserted by the telephone terminal, only activity messages can be sent and no B or D channel data is allowed onto the application module interface.
If the telephone terminal fails to detect the MOD-OK signal and receive an activity message from the module within 500 milliseconds of detecting the module present (MP) signal, the telephone terminal will disable its AMI transceiver and begin the start-up process over again. The start-up process should take at most 110 milliseconds, with 30 milliseconds allocated for detecting the module present (MP) signal, 50 milliseconds allocated for detecting five activity messages from the telephone terminal (during which time MOD-OK should be detected), and 30 milliseconds allocated for detecting the PHONE-OK signal.
The module waits up to one second from initialization to detect that the PHONE-OK signal has been asserted by the telephone terminal. If the one second time interval expires, the module should reset its AMI transceiver, turn off the MOD-OK signal, and begin the start-up process over again after a delay of at least 30 milliseconds.
Once the AMI connection has been established in accordance with the start-up process, the AMI connection may be disrupted, for example, due to a module losing power, being disconnected or a transient event that corrupts the data stream and causes a loss of synchronization. A disruption of the AMI connection may be detected using the hardware signals and the control channel protocol. If a disruption is detected, the detecting telephone terminal or module immediately turns off its receiving OK (PHONE-OK or MOD-OK) signal and disables its AMI transceiver. The detecting telephone terminal or module should then wait at least 30 milliseconds before attempting to restart the AMI.
According to an aspect of the invention, a number of mechanisms detect the disruption of the AMI connection. A telephone terminal or a module may detect that its counterpart receiving OK (PHONE-OK or MOD-OK) signal has been turned off. In addition, the telephone terminal may detect that the module present (MP) signal has been turned off.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.